This invention relates to the field of devices for use in operative surgery upon tissues of the body. More particularly, the invention relates to electrosurgical methods and systems for treatment of body tissues.
Electrosurgical devices use electrical energy, most commonly radio frequency (RF) energy, to cut tissue or to cauterize blood vessels. During use, a voltage gradient is created at the tip of the device, thereby inducing current flow and related heat generation in the tissue. With sufficiently high levels of electrical energy, the heat generated is sufficient to cut the tissue and, advantageously, to stop the bleeding from severed blood vessels.
Current electrosurgical devices can cause the temperature of tissue being treated to rise significantly higher than 100xc2x0 C., resulting in tissue desiccation, tissue sticking to the electrodes, tissue perforation, char formation and smoke generation. Peak tissue temperatures as a result of RF treatment of target tissue can be as high as 320xc2x0 C., and such high temperatures can be transmitted to adjacent tissue via thermal diffusion. Undesirable results of such transmission to adjacent tissue include unintended thermal damage to the tissue.
Using saline to couple RF electrical energy to tissue prevents such undesirable effects as sticking, desiccation, smoke production and char formation. One key factor is preventing tissue desiccation, which occurs if tissue temperature exceeds 100xc2x0 C. and all of the intracellular water boils away, leaving the tissue extremely dry and much less electrically conductive. However, an uncontrolled flow rate of saline can provide too much cooling at the electrode/tissue interface. This cooling reduces the temperature of the target tissue being treated, and the rate at which tissue thermal coagulation occurs is determined by tissue temperature. This, in turn, can result in longer treatment time, to achieve the desired tissue temperature for cauterization or cutting of the tissue. Long treatment times are undesirable for surgeons since it is in the best interest of the patient, physician and hospital to perform surgical procedures as quickly as possible.
RF energy delivered to tissue is unpredictable and often not optimal when using general-purpose generators. Most general-purpose RF generators have modes for different waveforms (cut, coagulation, or a blend of these two) and device types (monopolar, bipolar), as well as power levels that can be set in watts. However, once these settings are chosen, the actual power delivered to tissue can vary dramatically over time as tissue impedance changes over the course of RF treatment. This is because the power delivered by most generators is a function of tissue impedance, with the power ramping down as impedance either decreases toward zero or increases significantly to several thousand ohms.
A further limitation of current electrosurgical devices arises from size constraints of the device in comparison to tissue that is encountered during a single surgical procedure. During the course of a single procedure, for example, a surgeon often encounters a wide variety of tissue sizes. Surgical devices often come in a variety of sizes because larger segments of tissue physically require commensurately larger electrode jaws or tips, but smaller segments of tissue often are not optimally treated by the much larger size RF device. It is undesirable to require numerous surgical devices during a single procedure, because this wastes valuable operating room time, can make it difficult to precisely relocate the treatment site, increases the risk of infection, and increases the cost by increasing the number of different surgical devices that are needed to complete the surgical procedure.
For example, a bipolar saline-enhanced tissue sealing forceps that has jaws long enough to effectively seal a 30 mm length of tissue may not be desirable for sealing a segment of tissue that is 10 mm in length. Excess saline from one of the electrode jaws (for a bipolar device) can flow to the other electrode in the space where there is no intervening tissue. This flow of electrically conductive saline can act as an electrical resistor in parallel with the electrical pathway through the target tissue. Electrical current flow through the saline can divert or shunt RF energy away from going through the target tissue, and slow down the rate at which the target tissue is heated and treated.
A surgeon may first be sealing and cutting lung tissue as part of a wedge resection using the full 30 mm jaw length 2-3 times to remove a tip of a lobe of lung for biopsy. If the intraoperative histopathology indicates that the suspected tissue has a malignant tumor, then the surgeon may convert the procedure to a lobectomy. As part of the lobectomy the surgeon will want to seal and cut large blood vessels that supply the lobe. Alternatively, the surgeon may want to toughen up or coagulate large vessels with RF and then apply a ligating clip to assure hemostasis before cutting. Even compressed, these blood vessels might only fill a small fraction of the 30 mm length of electrode jaw. For at least the reasons identified above, this is an undesirable situation with current electrosurgical devices.
The invention provides a system for treating tissue comprising a power measurement device, a flow rate controller coupled to the power measurement device, and an electrosurgical device configured and arranged to provide radio frequency power and conductive fluid to the tissue, wherein the flow rate controller is configured and arranged to modify a flow rate of the conductive fluid to the tissue, based on signals from the power measurement device.
Preferably, the flow rate controller modifies the flow rate of the conductive fluid to the tissue based on heat used to warm the conductive fluid and heat used to convert the conductive fluid to vapor. In a preferred embodiment, the flow rate controller modifies the flow rate of the conductive fluid to the tissue using the relationship:   K  =      1          {                        ρ          ⁢                      xe2x80x83                    ⁢                      c            p                    ⁢          Δ          ⁢                      xe2x80x83                    ⁢          T                +                  ρ          ⁢                      xe2x80x83                    ⁢                      h            v                    ⁢                                    Q              b                        /                          Q              l                                          }      
In another embodiment, the invention provides a device for modifying flow rate of conductive fluid to tissue based on measurement of radio frequency power delivered to the tissue, the device comprising a flow rate controller configured and arranged to modify flow rate of the conductive fluid to the tissue, based on heat used to warm the conductive fluid and heat used to convert the conductive fluid to vapor. Preferably, the device modifies the flow rate of the conductive fluid to the tissue using the relationship:   K  =      1          {                        ρ          ⁢                      xe2x80x83                    ⁢                      c            p                    ⁢          Δ          ⁢                      xe2x80x83                    ⁢          T                +                  ρ          ⁢                      xe2x80x83                    ⁢                      h            v                    ⁢                                    Q              b                        /                          Q              l                                          }      
In an alternative embodiment, the invention provides a device for treating tissue using radio frequency power and conductive fluid, the device comprising a sensing device, and a processor coupled to the sensing device, wherein the processor is configured and arranged to adjust flow rate of the conductive fluid to the tissue, by determining a level of radio frequency power applied to the tissue using the sensing device, and adjusting the flow rate of the conductive fluid to the tissue. Preferably, the processor is configured and arranged to adjust the flow rate of the conductive fluid to the tissue based on heat used to warm the conductive fluid and heat used to convert the conductive fluid to vapor. Preferably, the flow rate controller modifies the flow rate of the conductive fluid to the tissue using the relationship:   K  =      1          {                        ρ          ⁢                      xe2x80x83                    ⁢                      c            p                    ⁢          Δ          ⁢                      xe2x80x83                    ⁢          T                +                  ρ          ⁢                      xe2x80x83                    ⁢                      h            v                    ⁢                                    Q              b                        /                          Q              l                                          }      
In another embodiment, the invention provides a method for treating tissue comprising applying radio frequency power and conductive fluid to the tissue using a surgical device, wherein the conductive fluid is provided to the tissue at a fluid flow rate, determining an amount of radio frequency power applied to the tissue, and modifying the fluid flow rate based on the power applied to the tissue. Preferably, the step of modifying the fluid flow rate based on the power applied to the tissue comprises modifying the flow rate of the conductive fluid to the tissue based on heat used to warm the conductive fluid and heat used to convert the conductive fluid to vapor. Preferably, the step of modifying the fluid flow rate based on the power applied to the tissue comprises determining the fluid flow rate using the relationship:   K  =      1          {                        ρ          ⁢                      xe2x80x83                    ⁢                      c            p                    ⁢          Δ          ⁢                      xe2x80x83                    ⁢          T                +                  ρ          ⁢                      xe2x80x83                    ⁢                      h            v                    ⁢                                    Q              b                        /                          Q              l                                          }      
In an alternative embodiment, the invention provides a method for treating tissue comprising providing a surgical device comprising an electrode, wherein the surgical device is configured and arranged to receive radio frequency power and conductive fluid and deliver the radio frequency power and conductive fluid to the tissue, determining the radio frequency power applied to the tissue, and providing the conductive fluid to the tissue at a fluid flow rate, wherein the fluid flow rate is modified to control boiling of the conductive fluid at the tissue. Preferably, the step of providing the conductive fluid to the tissue at a fluid flow rate comprises providing the conductive fluid to the tissue based on heat used to warm the conductive fluid and heat used to convert the conductive fluid to vapor. In a preferred embodiment, the step of providing the conductive fluid to the tissue at a fluid flow rate comprises providing the conductive fluid to the tissue using the relationship:   K  =      1          {                        ρ          ⁢                      xe2x80x83                    ⁢                      c            p                    ⁢          Δ          ⁢                      xe2x80x83                    ⁢          T                +                  ρ          ⁢                      xe2x80x83                    ⁢                      h            v                    ⁢                                    Q              b                        /                          Q              l                                          }      
In another embodiment, the invention provides a system for treating tissue comprising a power measurement device, a flow rate controller coupled to the power measurement device, a flow control device coupled to the flow rate controller, and an electrosurgical device coupled to the flow control device and the power measurement device, wherein the electrosurgical device is configured and arranged to provide radio frequency power and conductive fluid to the tissue, and wherein the flow rate controller is configured and arranged to modify a flow rate of the conductive fluid to the electrosurgical device, based on signals from the power measurement device. Preferably, the flow control device comprises a pump. In one embodiment, the pump comprises a peristaltic pump. In another embodiment, the pump comprises a syringe pump. Preferably, the electrosurgical device comprises a bipolar electrosurgical device.
According to this embodiment, the flow rate controller is preferably configured and arranged to modify the flow rate of the conductive fluid to the flow control device based on heat used to warm the conductive fluid and heat used to convert the conductive fluid to vapor. In a preferred embodiment, the flow rate controller is configured and arranged to modify the flow rate of the conductive fluid to the tissue using the relationship:   K  =      1          {                        ρ          ⁢                      xe2x80x83                    ⁢                      c            p                    ⁢          Δ          ⁢                      xe2x80x83                    ⁢          T                +                  ρ          ⁢                      xe2x80x83                    ⁢                      h            v                    ⁢                                    Q              b                        /                          Q              l                                          }      
The invention can improve the speed of tissue coagulation provided by fluid-enhanced electrosurgery by assuring that the electrode-tissue interface is within a desired temperature range (for example, not significantly hotter than 100xc2x0 C.) through the control of the fraction of conductive fluid that is boiled off at the electrode-tissue interface. This improvement can be achieved by measuring power provided to the device and regulating the flow of fluid to the device. Preferably, tissue sensors (for example, that would measure tissue temperature or tissue impedance) are not required according to the invention.
Some embodiments of the invention can provide one or more advantages, such as the ability to achieve the desired tissue effect (for example, coagulation, cutting, or the like) in a fast, effective manner. The invention can also provide the ability to treat tissue quickly without using a tissue sensor (for example, a temperature sensor) built into the device or a custom special-purpose generator. The invention can allow a surgeon to use a variety of electrosurgical devices with a wide variety of general-purpose generators. Further, the invention can provide the ability to use an electrosurgical device that is capable of quickly and effectively sealing a wide variety of tissue sizes and thicknesses.